Information about regional carbon sources and sinks can be derived from variations in observed atmospheric CO2 concentrations via inverse modelling with atmospheric tracer transport models. A consensus has not yet been reached regarding the size and distribution of regional carbon fluxes obtained using this approach, partly owing to the use of several different atmospheric transport models. Here we report estimates of surface-atmosphere CO2 fluxes from an intercomparison of atmospheric CO2 inversion models (the TransCom 3 project), which includes 16 transport models and model variants. We find an uptake of CO2 in the southern extratropical ocean less than that estimated from ocean measurements, a result that is not sensitive to transport models or methodological approaches. We also find a northern land carbon sink that is distributed relatively evenly among the continents of the Northern Hemisphere, but these results show some sensitivity to transport differences among models, especially in how they respond to seasonal terrestrial exchange of CO2. Overall, carbon fluxes integrated over latitudinal zones are strongly constrained by observations in the middle to high latitudes. Further significant constraints to our understanding of regional carbon fluxes will therefore require improvements in transport models and expansion of the CO2 observation network within the tropics.

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Towards robust regional estimates of CO2 sources and sinks using atmospheric transport models.

The modes of formation of carbonaceous deposits (“coke”) during the transformation of organic compounds over acid and over bifunctional noble metal-acid catalysts are described. At low reaction temperatures, ( 350°C), the coke components are polyaromatic. Their formation involves hydrogen transfer (acid catalysts) and dehydrogenation (bifunctional catalysts) steps in addition to condensation and rearrangement steps. On microporous catalysts, the retention of coke molecules is due to their steric blockage within the micropores.

Organic chemistry of coke formation

Surface chemistry of transition metal carbides.

Mimicking Aspects of Heterogeneous Catalysis: Generating, Isolating, and Reacting Proposed Surface Intermediates on Single Crystals in Vacuum.

Organic chemistry on solid surfaces

Benzene decomposition on the Rh(111) crystal surface has been studied over the temperature range of 300-800 K by high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED). Our results show that benzene decomposition begins at 400 K, forming a mixture of CH and C/sub 2/H species. The relative amounts of these two species vary with temperature; at 470 K, the concentration ratio of CH to C/sub 2/H is 0.4. Above 500 K, these fragments dehydrogenate and condense to form C/sub n/H polymers. By 800 K, the adsorbed monolayer is completely dehydrogenated, forming a polymeric carbon monolayer with a vibrational spectrum similar to that of an ordered graphite monolayer. The authors propose that benzene decomposition on Rh(111) proceeds by decyclotrimerization to form three acetylenes which immediately decompose to CH and C/sub 2/H species.

https://escholarship.org/content/qt0mh1g8tp/qt0mh1g8tp.pdf?t=p0wtyz

Thermal decomposition of benzene on the rhodium(111) crystal surface

The reactions of propylene, propadiene, and methylacetylene with Rh(111) crystal faces in ultrahigh vacuum (UHV) from 80 to 800 K have been studied by low-energy electron diffraction (LEED), high-resolution electron energy loss spectroscopy (HREELS), and thermal desorption spectroscopy (TDS). All three hydrocarbons adsorb intact at 80 K. At this temperature, methylacetylene forms a p(2 x 2) LEED pattern while propylene and propadiene adsorb as disordered monolayers. Above 200 K, propylene and propadiene also form p(2 x 2) LEED patterns which are stable up to 270 K. The propylene fragment in this temperature range is propylidyne (CCH/sub 2/CH/sub 3/). By room temperature all the C/sub 3/ hydrocarbons have decomposed to ethylidyne (CCH/sub 3/) and polymerized C/sub x/H fragments. Surface hydrogen is instrumental in the C-C bond breaking, and partial deuteriation studies were performed to determine which C-C bonds break first. The ethylidyne species are stable up to 400 K, above which they decompose to C/sub x/H fragments. The bonding and the thermal decomposition pathways for propylene on Rh(111) are compared to Pt(111) surface chemistry.

https://escholarship.org/content/qt7k52t854/qt7k52t854.pdf?t=p0jv95

B. E. Bent

Papers

Thermal decomposition of benzene on the rhodium(111) crystal surface

Bonding and thermal decomposition of propylene, propadiene, and methylacetylene on the Rh(111) single-crystal surface